The vertebral column of the human skeletal frame, often called the spinal column, is formed of a series of bones called vertebrae. It is a flexible column. The head is balanced on top of the column. The skeletal framework of the neck consists of seven cervical vertebrae. In the cervical region of the spinal column, extension, abduction and rotation (twisting) are more extensive than in any other region. The neck has interior, lateral and posterior groups of muscles to provide and control the versatile movement permitted by the cervical vertebrae. Because of the free mobility of the cervical vertebrae compared with that of the thoracic and lumbar areas, severe neck injuries, while relatively uncommon, require therapeutic treatment that includes immobilization of the cervical region. The neck has been known to be broken (fractured) and dislocated, especially in football and diving. Any severe force that either hyperextends, compresses or twists the neck can cause cervical fracture. Cervical dislocations most often occur at the fourth, fifth or sixth vertebrae. Less severe, but nonetheless significant, injury, occurs upon hyperextension of muscles of the interior, lateral and posterior groups. Upon occurrence of such injuries, the neck requires at least some degree of immobilization in order to heal. Two forms of neck braces or cervical collars are popular. The first provides a pair of relatively rigid halves that come together about the neck and are fastened in some fashion to immobilize the neck. The other involves simply a cervical collar of a soft material such as a low density foam that gives minimal support.